1. Field of the Invention
This invention relates to a solar heating device of the small portable type the primary use of which is cooking, and to a heating process utilizing solar energy.
2. Prior Art
While this invention can be used for heating liquids and gases, such as air, the principal utility of the device and process is for cooking.
Prior solar cookers have been of four principal types.
The simplest type of prior solar cooker is of the box type such as represented by Kerr U.S. Pat. No. 4,236,508, issued Dec. 2, 1980, which includes a box open at the top for holding food to be cooked and having a cover hingedly attached to one upper edge of the box for reflecting solar rays down into the open top of the box oven. With such a box, the rays of the sun are not sufficiently concentrated to create a temperature high enough to cook food effectively.
The second type of solar cooker is the concentrated focus type represented by the Von Brudersdorff U.S. Pat. No. 2,859,745, issued Nov. 11, 1958. The solar rays are concentrated by a double-curved concave reflector which concentrates the solar rays on a relatively small focus area so that either the size of the cooking area is smaller than desirable or the double-curved concave reflector must be larger than desirable.
A third type of prior solar cooker is shown in the Andrassy U.S. Pat. No. 3,938,497, issued Feb. 17, 1976, which directs solar rays onto a plate having a comparatively large area both by a cylindrically concave type of reflector and by flat plates. The plate to be heated may have heat-collecting fins and transfers heat to food to be cooked or to water to be heated.
The fourth type of solar cooker is of the line focus type which is the type to which the present invention relates. Line focus cookers are represented by the Fischer U.S. Pat. No. 4,083,357, issued Apr. 11, 1978, the Ilich U.S. Pat. No. 4,262,660, issued Apr. 21, 1981, and the Takeuchi et al. U.S. Pat. No. 4,442,828, issued Apr. 17, 1984. The cookers of the Fischer and Ilich patents have reflectors of parabolic shape, whereas it is not clear whether the composite reflector of the Takeuchi et al. patent is of parabolic shape or of cylindrically curved shape like the reflector of the Andrassy patent. In any event, the reflectors of all of the Fischer, Ilich and Takeuchi et al. patents concentrate solar rays along a line focus, as distinguished from an area focus as utilized by the cooker of the Andrassy patent, or from a more localized focus as in the cooker of the Von Brudersdorff patent having a double-curved concave reflector.
A disadvantage of the line focus type of solar cookers shown in the Fischer, Ilich and Takeuchi et al. patents is that they utilize only direct solar rays collected over an area substantially equal to the area of the reflector which requires much larger apparatus to obtain a predetermined heating effect than is obtained by the device of the present invention.